1. Field of the Invention
The present invention is generally related to laser eye surgery systems, devices, and methods. In particular, the present invention provides an adjustable focus patient fixation system which can accommodate refractive errors in a patient's eye, presenting a target which appears to the eye to be in focus, and thereby enhancing the patient's ability to stabilize the eye by viewing the target. In some embodiments, the present invention allows patients to maintain accurate focus and enhanced stabilization on a viewing target during changes in the refractive characteristics of the eye by coordinating focus adjustments of the target system with a photorefractive therapy. Hence, the present invention is particularly useful for enhancing the accuracy and efficacy of laser eye surgical procedures such as photorefractive keratectomy (PRK), phototherapeutic keratectomy (PTK), laser in situ keratomileusis (LASIK), and the like.
Selective photoablation of corneal tissues benefits from precise alignment between the eye and a therapeutic laser beam. Known laser eye procedures generally employ an ultraviolet or infrared laser to remove a microscopic layer of stromal tissue from the cornea of the eye to alter its refractive power. The laser removes a selected portion of the corneal tissue, often to correct refractive errors of the eye. Ultraviolet laser ablation results in photodecomposition of the corneal tissue, but generally does not cause significant thermal damage to adjacent and underlying tissues of the eye. The irradiated molecules are broken into smaller volatile fragments photochemically, directly breaking the intermolecular bonds.
Laser ablation procedures can remove the targeted stroma of the cornea to change the cornea's contour for varying purposes, such as for correcting myopia, hyperopia, astigmatism, and the like. Control over the distribution of ablation energy across the cornea may be provided by a variety of systems and methods, including the use of ablatable masks, fixed and moveable apertures, controlled scanning systems, eye movement tracking mechanisms, and the like. These laser eye surgery systems are adapted for use while the patient is awake. The position of the patient's head will often be stabilized using a headrest pillow, a chin rest, a bite bar, or the like. The patient can further enhance alignment between the eye and the therapeutic laser beam by focussing on a target during the procedure.
Known visual fixation targets typically include a light emitting diode (LED) which is optically positioned about 1/4 meter in front of the patient. Unfortunately, patients do not wear corrective lenses during photorefractive surgery. As a result, the target may be blurred or out of focus for many patients. Even more problematic, the optical characteristics of the patient's eye may change significantly during laser eye surgery. As a result, the patient's ability to hold her eye steady by viewing the target can be compromised. In fact, patients have reported losing site of the blurry targets during laser eye surgery. This may cause the patient to look away from the target, degrading alignment between the laser eye system and the eye, and thereby decreasing the accuracy and efficacy of the refractive therapy.
In light of the above, it would be desirable to provide improved ophthalmological systems, devices, and methods. It would be particularly desirable to provide enhanced techniques for stabilizing an eye having a significant refractive error throughout a laser eye surgery procedure. It would further be desirable to provide enhanced methods and devices for initially establishing and maintaining alignment with a patient fixation system to provide enhanced eye stabilization before and during laser eye surgery and other therapeutic or diagnostic procedures for the eye.
2. Description of the Background Art
U.S. Pat. No. 4,478,449, describes an operation microscope which incorporates an eye fixation device. U.S. Pat. No. 5,549,597, describes an in situ axis alignment module for determining the astigmatic axis of a patient, and for aligning the cylindrical axis of a laser ablation system for ophthalmological surgery.
U.S. Pat. No. 5,258,787, describes an ophthalmologic apparatus having an illumination optical system for directing light onto a prescribed point of an eye, and an observation optical system for observing an image of the prescribed point. U.S. Pat. No. 5,557,352, describes a method and apparatus for measuring the visual acuity and refraction of the human eye during and immediately after ocular surgery.